What solutions are there for flexible batch sizes (powdery goods) from 5 to 5,000 litres within the same mixer type?
Processing batches between 5 and 5,000 litres places high demands on mixing technology and process development. Two questions must be distinguished here. The first concerns the minimum and maximum fill quantity that a single mixer can usefully process. The second concerns the transferability of a mixing process from a laboratory unit to larger production mixers of the same series.
A single mixing machine usually cannot usefully cover a range from 5 to 5,000 litres. That corresponds to a ratio of 1 to 1,000. With very small fill quantities, mixing tools cannot immerse sufficiently into the product. In addition, wall friction, residual quantities, dischargeability and cleaning effort become much more significant for small batches. In practice, therefore, a geometrically and functionally comparable mixer series with laboratory, pilot and production mixers is usually the better solution.
Vertical mixing systems with a conical vessel geometry are particularly suitable for strongly varying fill levels. Conical screw mixers based on the Nauta principle guide the product to the lowest point of the vessel. This allows an orbiting screw to remain effective on the product even at comparatively low fill levels. Vertical single-shaft or twin-shaft mixers with large-area mixing tools operating close to the base can likewise cover a wide fill-level range. However, whether a specific minimum fill quantity is achieved always depends on the bulk material, particle size, bulk weight, flow behaviour, mixing task and tool geometry.
High flexibility within a single machine requires a suitable vessel and mixing-tool geometry. Conical bases or specifically designed base geometries ensure that sufficient product remains within the effective range of the mixing tool even at partial fill. Tools positioned close to the base can improve product movement in the lower region and reduce the formation of stagnant zones.
Frequency-controlled drives make it possible to adapt rotational speed and mixing intensity to fill level and product properties. A lower speed can protect sensitive particles, while a higher speed accelerates mixing for certain tasks. However, the required speed must not be derived solely from a constant specific power input. For dry bulk materials, gravity, wall friction, particle shape and cohesion also determine mixing behaviour.
Good dischargeability is particularly important for small batches. Low-dead-space outlet fittings and a structurally favourable vessel geometry reduce residual quantities. The smaller the batch, the greater the percentage impact of product residues on yield, recipe fidelity and cross-contamination. If the product needs to be temperature-controlled, an adapted heating or cooling design can be useful. For powdery goods, however, it must be checked whether heat transfer is adequate at low fill levels.
In practice, the range from 5 to 5,000 litres is covered by a mixer series with several sizes. For a robust scale-up, the mixers should be comparable in their basic geometry and mode of action. This includes, among other things, the ratio of mixing tool to vessel diameter, the vessel height, the position of the tools and the type of product movement.
For scale-up, characteristic values such as peripheral speed, Froude number, specific power input or energy input can serve as orientation. However, these values cannot all be held constant at the same time. Which parameter is decisive for the transfer depends on the mixing task. For free-flowing bulk materials, convective product movement is often the priority. For cohesive, moist or agglomerate-containing powders, shear action, mixing time and the design of size-reduction tools can be more important.
A geometrically similar mixer series reduces development effort, but does not replace trials at pilot or production scale. Differences in fill level, product pressure, bulk weight, emptying and addition time can influence mixing quality. Critical recipes should therefore be trialled with the original product across several sizes. In addition to mixing quality, segregation tendency, gentle product handling, residual emptying, cleanability and reproducibility are also assessed.
The economically and process-engineering sensible solution usually consists of a consistent mixer series for laboratory, pilot plant and production. This is supplemented by mixers with as large a usable fill-level range as possible, frequency-controlled drives, low-dead-space emptying and a mixing-tool geometry matched to the product. This makes it possible to produce development batches, pilot quantities and production batches with comparable mixing action, without exceeding the physical limits of a single machine.
Batch ranges and sizes: amixon® mixing technology from 5 litres to 100 cubic metres
amixon® offers mixing solutions for development batches, pilot quantities and large-volume production batches. The range extends from small single-shaft mixers starting at around 5 litres to large Gyraton® mixers for batches of up to around 100 cubic metres. What matters here is not just the nominal volume, but the question of at what fill level, with what product, and in what time a defined mixing quality is to be achieved.
High flexibility within a single mixer
Many amixon® mixers can cover a wide fill-level range. Depending on the mixer type, product and mixing task, fill levels of roughly 10 to 100 percent of the usable capacity are possible. This allows a production mixer to process different lot sizes without requiring a separate plant for every batch size.
An HM 7000, for example, can process both partial batches and the full nominal batch, given a suitable recipe and design. However, whether the same mixing time and mixing quality are achieved at 800 litres and at 7,000 litres must be verified with the original product. A wide fill-level range reduces the need for a second machine, but does not replace the process-related assessment and, where applicable, qualification of different batch sizes.
The amixon® size range
Single-shaft mixers of the EM series are suitable for development, small and just-in-time batches. Depending on the design, standard drums can be used as mixing vessels. This facilitates the processing of small quantities and can avoid transfer steps.
Container mixers of the COM series use the Mixtainer or IBC as the mixing chamber. They cover batches of roughly 100 to 4,000 litres and are particularly suitable for processes in which the container is used simultaneously as a transport, storage and mixing vessel.
Vertical mixers and conical mixers of the VM, HM and AM series, as well as vacuum mixer-dryers and reactors of the VMT and AMT series, are available in numerous sizes. This allows plant capacity to be closely matched to the required batch size. Special designs also enable large usable volumes of up to around 50,000 litres.
The Gyraton® GM is available for large batches. It can be designed for batches in the range of roughly 10 to 100 cubic metres. The specific size is determined on the basis of the product, the required mixing time, fill level, installation situation and material logistics.
In addition, amixon® offers continuous mixing and granulating solutions. These are useful where the priority is not individual batches but a steady mass throughput. The choice between batch and continuous process depends on the recipe, throughput, cleaning requirements and the required degree of flexibility.
Throughput results from the entire process
The actual throughput of a mixing plant does not result from batch size alone. Mixing time, filling, dosing, emptying, cleaning and switching between recipes are all decisive. amixon® therefore views cycle time as an overall process.
Fast and as complete as possible emptying can significantly improve plant availability. The KoneSlid® KS enables fast product discharge. ComDisc® elements support residual emptying and help reduce the risk of segregation during discharge. The achievable emptying time and residual quantity depend on the product and the specific plant configuration.
Scaling with pilot-plant trials
amixon® series are designed so that the respective mixing task can be transferred systematically from development to production. Within a mixer series, the basic mode of mixing action and the product-effective elements remain comparable. Nevertheless, a scale-up is not guaranteed by geometric similarity alone.
Mixing trials with the original product are therefore a central part of the design process. The amixon® pilot plant in Paderborn has more than 30 test units available in various sizes. Additional pilot facilities exist in Japan, India, Thailand, China, South Korea and the USA. Trials can be carried out at realistic fill levels, batch sizes and the intended temperature and pressure conditions.
Mixing quality, gentle product handling, energy input, dischargeability, cleanability and reproducibility are evaluated. The results form the basis for selecting the size and defining the process parameters for later series operation.
Hygienic design for batch changeover
The amixon® Hygienic Design supports fast product changeovers and good cleanability. The mixing chamber and mixing tool are seamlessly welded and ground. The mixing tool is supported only at the top. This eliminates the need for a product-contact lower shaft feed-through.
Clever-Cut® inspection doors with OmgaSeal® seals provide good access to the product-contact surfaces. Low-dead-space outlet fittings and optionally integrated wash lances support dry or wet cleaning. Depending on the application, the design can be adapted to the hygiene requirements of the food, pharmaceutical or chemical industry.
amixon® therefore does not offer a single machine for the entire range from 5 to 5,000 litres, but a coordinated modular system. It combines flexible fill levels within individual mixers with a wide selection of sizes and process-realistic trials in the pilot plant.